In recent years, thin film devices that employ organic semiconductors such as an organic EL device, an organic FET device, and an organic thin film converting device have been considered noteworthy, and some of the thin film devices have been put into practical use. A fundamental and important property of the organic semiconductors for use in these thin film devices is electron field-effect mobility (carrier mobility).
For example, in organic EL devices, the electron field-effect mobility affects charge transport efficiency and is important to realize highly efficient light emission and a low voltage drive. Further, in organic FET devices, the electron field-effect mobility directly affects switching speed and performances of a device to be driven. Therefore, for practical use of the organic FET devices, it is quite important to improve the electron field-effect mobility.
Generally, such organic semiconductors have a low electron field-effect mobility compared with silicon semiconductors, and this prevents practical use of the organic semiconductors. However, recent developments of new organic semiconductor materials have realized organic semiconductors having as high an electron field-effect mobility as that of amorphous silicon.
As the organic semiconductor materials, a material using an existing compound and a material in which an existing compound is modified are conventionally used. For example, polyacene such as pentacene is used as a material of a semiconductor layer. In such an acene material, which is a fused polycyclic aromatic compound, a greater number of fused rings (fused-ring number) provides a better electron field-effect mobility to an organic semiconductor using the material. This is because this provides greater π electron orbits thereby strengthening an intermolecular interaction. In view of this, the increase of the fused-ring number is an effective method to improve the electron field-effect mobility of the organic semiconductors.
However, the increase of the fused-ring number makes it difficult to dissolve the material of a semiconductor layer, or causes a decrease in stability. Although the problem of solubility does not become a significant problem for a deposition material, the remarkable decrease in stability in the atmosphere is a significant hindrance to practical use of the material. In view of this, there is demand for a new material design for solving these problems.
Inventors of the present invention have already found a benzodichalcogenophenobenzodichalcogenophene (hereinafter, referred to as “BXBX”) material. As disclosed in Patent Literature 1, the BXBX material successfully has a high stability and a transistor characteristic (high electron field-effect mobility, large on/off ratio, low threshold and swing).
In order to produce a material having more fused rings and find a more excellent material by extending the above finding, it is also an option to produce (a) a compound including: a BXBX skeleton further having an aromatic ring outside the BXBX skeleton, or (b) a compound including a BXBX skeleton in which a benzene ring is substituted with a heterocyclic ring. For example, Patent Literatures 2 and 3, and Non Patent Literatures 1 through 11 disclose methods for producing the compound including a BXBX skeleton in which a benzene ring is substituted with a heterocyclic ring.
Non Patent Literature 12 discloses a compound represented by Formula (2) of the present invention, where X1 and X2 are sulfur atoms, and R1 through R12 are hydrogen atoms. However, Non Patent Literature 13 discloses that the structural formula of the compound is erroneously recited in Non Patent Literature 12, and the compound is a structural isomer of Formula (2) of the present invention.
However, the conventional methods disclosed in Patent Literatures 2 and 3, and Non Patent Literatures 1 through 11 needs multistage synthesis in which molecules are required to be built up via multiple stages. Therefore, these methods are too troublesome for practical use. That is, there has not been yet established a method for easily producing an organic semiconductor material that can attain a sufficient electron field-effect mobility.